But anyway, an office building, eh? Which office building? Are we talking Pentagon-size? The Pentagon, you know, is the world's largest office building. Obviously, this asteroid isn't Pentagon-sized or the WaPo would have said an asteroid the size of the Pentagon, which would have sounded much more amusing (and scary) than "office-building-size asteroid," which leads me to picture an ordinary place downtown in my own city.

So, I'm picturing it, this office-building-size asteroid. What happens if it hits?

How big must we go before we're talking wiping-out-the-dinosaurs apocalypse? Apparently, that would be about 5 miles wide. And, no, the Pentagon is not 5 miles wide. It's 921 feet along each outer side facade.

ADDED: A reader writes:

While the physics that I do for a living doesn't have a whole lot to do with planets or asteroids, I do enjoy the stuff and am fairly well versed in it. Since you were wondering on the blog today what a 150 foot asteroid would do, it's about half the length of the asteroid that did the Tunguska event. Remember that mass goes more or less like length-cubed, so the 150 foot asteroid would be about 1/8th the weight/power.

Tunguska had the power of 1000 Hiroshima bombs. So 1/8th of that still would more or less destroy a city if it landed on it. Most likely, of course, any asteroid would hit the ocean. But that would still cause a massive tsunami like we haven't seen in recorded history.

I don't know if you've heard of the Apophis asteroid, but it's more than 3x the length of the Tunguska asteroid and it's going to come very close to Earth in 2029, and then again in 2036 (though it will not hit either year, it's still been mixed in with a lot of silly 2012-style apocalypse myths). Scientists have already accomplished the task of landing a spacecraft on another asteroid, so there is a lot of talk of attaching a beacon to Apophis in 2029 so we could follow it on its path. Would be really fascinating science.

It's diameter is about half the length of a football field. So it's maybe the size of a small office building, or a very large (Biltmore category) house.

The asteroid will pass right through the outer Van Allen radiation belt. It will be interesting to see if it disrupts the ions there, triggering aurorae. Folks who live in the northern states and Canada might watch that night to see. The skies will have to be cloud-free, of course

yeah, it won't hit us this time, but it keeps trying and will be back in a few decades. And if something hits it in the meantime the size of a bus, well then the orbit may not be as friendly as predicted next time.

To put those scales in context, This rock is coming in at about 7% of thedistance to the moon.

By the way, take a look at the Moon sometime through a telescope. You'll see thousands of craters, some fairly recent.

Every one of those craters is the result of a chunk of rock that didn't hit the Earth. We humans owe our existence to the Moon, which has protected the Earth from millions of rocks like this, or larger, over the past 4.6 billion years. Too bad for the dinosaurs, one big one got past the Moon about 65 million years ago.

An asteroid impact would make you listen to weeks of stupid news about it beforehand.

Not necessarily. In many of these close encounters, we only learned about them only a short time before or sometimes just after they happened. There are a small number of automated telescopes dedicated to detecting and cataloging near Earth objects. However, there are still big gaps in the coverage.

The usual disaster scenario we hear about is an asteroid hitting earth; but clearly an asteroid could miss earth, but smash up a bunch of satellites. I've not heard anyone talk about the consequences of that.

Another idea occurs to me: what if we towed a couple of asteroids to earth, and got them spinning in orbit, adding two moons. Would that significantly increase our protection? I realize it would have other effects--and cost a bunch of money--but it would be interesting to see someone explore the idea.

"And if something hits it in the meantime the size of a bus, well then the orbit may not be as friendly as predicted next time."

Something could well hit it today or tomorrow or the next day. Wouldn't take much of a nudge to have end up as a permanent part of our landscape. And the sooner that nudge occurs, the less force it will have to impart to result in a path that neatly intersects ours. It may not even rise to the level of Tunguska, but it should make people think about how much money is being spent on this issue as opposed to things like carbon footprints (or cancer, or Alzheimer's, or...). A big enough rock will make all of those other issues moot. Extremely moot. And it is only a matter of time.

yeah, it won't hit us this time, but it keeps trying and will be back in a few decades. And if something hits it in the meantime the size of a bus, well then the orbit may not be as friendly as predicted next time.

This and the possibility of another Carrington Event pose a far greater threat than the mythical AGW and we aren't prepared at all for either event.

Fr Martin Fox:Another idea occurs to me: what if we towed a couple of asteroids to earth, and got them spinning in orbit, adding two moons. Would that significantly increase our protection? I realize it would have other effects--and cost a bunch of money--but it would be interesting to see someone explore the idea.

In order to significantly increase our protection, the asteroid(s) would have to be significantly massive, which would significantly increase both the cost and the "other effects," including the tides. Probably not worth it, in the end. :)

I had a dream last night that a massive asteroid struck an ancient, water-covered Mars. The wound was deep enough to hit its molten metallic core, or triggered a deeper fracture which did. Molten iron slowly oozed out and reacted with water:

2Fe + 3H2O = Fe2O3 + 3H2

(there may have been some peroxide catalysis involved)

The hydrogen eventually escaped Mars' gravity and all the water was used up, leaving a thin skin of rust on the whole planet which explains its red color.

It depends on the type of communicatons satellite. The most common and widely known are those out at geosynchronous orbit, as described above. There are also communications satellites (including US ones but mostly Russian ones) in inclinded, highly-elliptical Molniya orbits.

There are also constellations of communications satellites like Iridium and GlobalStar in high inclination low Earth (300-500 miles) orbits. These allow very wide area coverage for special handheld phones.

Every one of those craters is the result of a chunk of rock that didn't hit the Earth. We humans owe our existence to the Moon, which has protected the Earth from millions of rocks like this, or larger, over the past 4.6 billion years. Too bad for the dinosaurs, one big one got past the Moon about 65 million years ago.

While it's true that all the rocks that hit the Moon therefore didn't hit the Earth, it's not the case that “We humans owe our existence” (at least for that reason) to the Moon. Because the Earth is larger than the Moon in cross-section and its gravity is much larger and spread over a far greater volume of space, many more (and larger) rocks were drawn in to hit the Earth than hit the Moon! It's just that Earth's active geology over eons of time eroded away almost all of those impact basins, whereas the Moon is geologically quiescent (except for further impacts) and did not.

@Astro -- no, the moon does not "protect" us, because its gravitational attraction is about 15% that of Earth. You see craters all over the moon because there is no air or water to erode them.

Here on Earth we've been hit (hard) plenty of times, most notably the Vredefort Crater in South Africa, which resulted from an asteroid some 10 km in diameter about 2000 million years ago. The crater is about 300 km across.

Wilkes Land in Antarctica is vastly larger, but a bit difficult to study because it's buried under a shitload of ice.

Or the Manicouagan crater in Québec, which is only about 200 million years old and much more obvious. It's also an astoundingly good canoe trip around that lake (you can drive there in summer), and Québec overall is a remarkable place for a vacation.

Don't worry too much about the French language thing. They take excellent care of tourists from the States. If you're from Ontario, however, and don't make at least an effort to speak French they will immediately forget every word of English they ever knew.

It's worth noting in this regard that asteroids are not the only (significantly probable) danger to Earth from outer space — there are also the comets. Comets originate far beyond the (planetary) solar system, out in the Oort Cloud (though some may come from the somewhat-closer-in Kuiper Belt), where occasionally such a body (a drifting ice ball) will get perturbed into a new orbit which happens to enter the inner solar system and where it can endanger Earth. While many such comets get further deflected by planetary gravitational fields into short and medium-term orbits where we can see them and (somewhat) predict their futures vis-a-vis Earth, newcomers here for the first time cannot be foreseen in this way (whereas essentially all of the asteroids can).

"I had a dream last night that a massive asteroid struck an ancient, water-covered Mars. The wound was deep enough to hit its molten metallic core, or triggered a deeper fracture which did. Molten iron slowly oozed out and reacted with water:

You see craters all over the moon because there is no air or water to erode them.

Also no plate tectonics to subduct them, nor to raise and crumple them up into an unrecognizable range of mountains — nor are there sediments on the Moon (other than the result of yet further impacts) to bury them.

And thanks for the list of craters, Bart! But, one you overlooked is the dinosaur-killer crater itself — known as Chicxulub, and located down on the Yucatan Peninsula of North America.

Though presently buried beneath a kilometer of sediments, you can see what that 180 km (112 miles) in diameter crater still looks like today (obtained via gravity measurements).

An exercise left for the reader. If the speed of light is 670,616,629 mph (and I gather that it is) and geosynchronous satellites are in orbit 22,240 miles above the mean sea level, and radio frequency signals travel at the speed of light (they do) how long does it take a signal to do the round trip to a communications satellite and back?

Of course I balanced the equation as an afterthought while fully awake. That is my curse. But it made me ask whether that reaction is thermodynamically feasible. Unfortunately, most tabulated thermodynamic data is for STP conditions which are terrestrial and not at all martian.

The south rim of Chicxulub BTW could be an awfully good place to prospect for rare-earth elements because that degree of impact might have released some magma or at least melted enough silicate and basic material to have generated a few good carbonatite deposits.

Disclosure: my first two degrees were in geology and geochemistry, so this kind of stuff is conversation over beer in the right circles.

Big Mike: Slightly related, GPS satellites have to take into account relativistic effects in keeping time. They have onboard clocks that supposedly keep time accurately to within a nanosecond. But their motion relative to the Earth causes their clocks to run more slowly than one on the Earth by 7,200 nanoseconds per day, and the weaker gravitational field they are in causes them to run faster by 45,900 nanoseconds per day (so presumably there is a net result of their clocks running 38,700 nanoseconds faster every day). If they stop accounting for these effects, the GPS satellites would give unusable results within 1.5 minutes (this info from Neffe's biography of Einstein).

Fr Martin Fox said...The usual disaster scenario we hear about is an asteroid hitting earth; but clearly an asteroid could miss earth, but smash up a bunch of satellites. I've not heard anyone talk about the consequences of that.

Another idea occurs to me: what if we towed a couple of asteroids to earth, and got them spinning in orbit, adding two moons. Would that significantly increase our protection? I realize it would have other effects--and cost a bunch of money--but it would be interesting to see someone explore the idea.

Think billiard balls. The angle of reflection is equal to the angle of incidence. You run the risk of having two objects hitting the earth.Plus the added danger of having another mass, like the moon, screwing with the tides.

Comparing the relative size of our moon to the moons of other planets, our moon is enormous. This size acts not only to sweep up many rocks that otherwise might have hit the earth, but (from what I'd heard) the gravitational dynamics of the moon-earth system tends to move rocks away from the earth rather than toward it. Perhaps this is due to most solar system objects having posigrade rather than retrograde motion around the sun.Jupiter is said to play the same kind of role, protecting the inner solar system from Oort Cloud objects.

Sean, In amateur radio, when communicating in morse code it is possible on rare occasions to to hear your own transmissions as an echo if you are lucky enough to have the signal travel all the way around the world back to you.

As a radar tech in the Navy I learned that a "radar mile" is approx 12.3 micro second. that's the time it takes the radar signal to travel the distance to and from an object that is one mile in distance away.

So just multiply that times the distance in miles from the given object and you can determine the time element.

Bill Bryson's book "A Brief History of Everything" has a chapter on meteor strikes. Suffice it to say that it presents the occurrence as nearly inevitable and very, very bleak. It wouldn't take much of a meteor to really louse things up, and there are lots and lots of them out there, most of which we don't even know about.

Big Mike said... An exercise left for the reader. If the speed of light is 670,616,629 mph (and I gather that it is) and geosynchronous satellites are in orbit 22,240 miles above the mean sea level, and radio frequency signals travel at the speed of light (they do) how long does it take a signal to do the round trip to a communications satellite and back?

Your example seldom happens in the real world because your numbers only work if the satellite is directly over you. For most people, the slant range to the satellite is considerably longer because a) the people are not on the equator and b) the satellite is usually at a different longitude than the user. It's a non-trivial spherical geometry problem to find the range to and from the satellite. Also, there isn't much point in sending signals to yourself, so you have to also factor in the location of the other antenna on the ground to get the total distance.

Is there anything we can do to prevent this? I mean, how can we temp this dude into slamming us good and hard, cause that's what I'd call good news. We need a good shaking up, a jostle, a good rodgering, if you will.

We need to get our sexy on, and quick. We don't have much time before he sees Venus. That smokey hot bitch will lure him right in, and bang! - satisfaction right in the habitable zone, and us just watching as we sit in the corner like Larry Flint with our sweet memories of turning such things down because we had better stuff to do.